Chemical reactions are simply the combination or
fragmentation of groups of atoms whose movement is governed by
the molecular potential energy surface. We have developed a new
method for constructing such a surface from ab initiio
quantum chemistry calculations, so that the dynamics of chemical
reactions can be studied and understood.

What are the basic questions addressed?

How efficiently can we construct a molecular potential
energy surface (PES) by interpolation of local Taylor expansions
of the surface? How can the process be optimised?

What are the results to date and future of the
work?

Truncating the local Taylor expansions at second
order is computationally most efficient, while we have also shown
that if the ab initio calculation of third order derivatives
of the electronic energy can be improved in efficiency, then third
order expansions should prove to be superior in accuracy and computational
efficiency. The ab initio calculation of a surface (at
the Hartree-Fock level of theory) for the OH + H2 Æ
H2O + H reaction has been accomplished. Further development of
the methodology is required for applications to larger systems.

What computational techniques are used and why
is a supercomputer required?

Two aspects of this project benefit from a supercomputing
environment: ab initio quantum chemistry calculations and the
use of classical trajectories in building the surface and evaluating
the dynamics.